The Friction And Wear Of Ceramic/ Ceramic And Ceramic/Metal . - NASA
DOE/NASA/50306-3 NASA TM-106348 The Friction and Wear of Ceramic/ Ceramic and Ceramic/Metal Combinations in Sliding Contact Harold E. Sliney and Christopher DellaCorte National Aeronautics and Space Administration Lewis Research Center (NASA-TM-106348) THE FRICTION WEAR OF CERAMIC/CERAMIC AND CERAMIC/METAL COMBINATIONS IN SLIDING CONTACT (NASA) 13 p October 1993 Prepared for U.S. DEPARTMENT N94-15769 AND Uncl G3/Z] OF ENERGY Conservation and Renewable Energy Office of Vehicle and Engine R&D as 0191152
THE FRICTION AND CERAMIC/METAL WEAR OF CERAMIC/CERAMIC COMBINATIONS Harold National IN SLIDING AND CONTACT E. Sliney and Christopher DellaCorte Aeronautics and Space Administration Lewis Research Center Cleveland, Ohio 44135 SUMMARY sliding The tribological characteristics of ceramics sliding on ceramics are compared to those of ceramics on a nickel-based turbine alloy. The friction and wear of oxide ceramics and silicon-based ceramics in air at temperatures from room ambient to 900 C (in a few cases to 1200 C) were measured for a hemispherically-tipped pin on a flat sliding contact geometry. In general, especially at high temperature, friction and wear were lower for ceramic/metal combinations than for ceramic/ceramic combinations. The better tribological performance for ceramic/metal combinations is attributed primarily to the lubricious nature of the oxidized surface of the metal. INTRODUCTION Ceramics are serious contenders point, chemical inertness, and in some heat rejection diesel engine and turbine oxidative attack at high temperature. ponents requiring low dynamic inertia for use as bearing and seal materials because of their high melting cases their low density. High melting point is important in low engine applications. The oxide ceramics, in particular are inert to The light weight of some ceramics is especially attractive for comsuch as those in valve trains. Reported results of tribological studies of ceramic/ceramic combinations have been disappointing. Friction coefficients are generally high, on the order of 0.5 to 1.0 (refs. 1 and 2). Also, wear rates are often high in spite of a polished surface finish prior to sliding and the high hardness level of many ceramics. A frequently observed wear mode is one of microfracture, typically grain boundary fracture. The causative factors for this wear mode in ceramics appear to be low tensile strength coupled with low ductility and high friction. Friction during sliding generates tensile stresses in the plane of the sliding surface (refs. 3 and 4). These tensile stresses initiate cracks that propagate along grain boundaries. The grains debonded from the structure work out of the surface in the form of microfracture wear debris that is further pairs attrited during continued It is the purpose of this paper with those of ceramic/ceramic sliding. to compare the friction and wear properties pairs. Some metal alloys are known to form of ceramic/metal sliding oxide surface films that are lubricous at high temperature. For example, some nickel base and cobalt base turbine much lower friction and wear in air at high temperature than at low temperature because alloys exhibit of the lubri- cating property of their naturally formed oxides when hot (ref. 5). Also, it has been shown that doping of certain ceramics by ion mixing with metals that form lubricous oxides reduces high temperature friction compared to the undoped ceramic (ref. 6). Further, recently reported studies show that alloying ceramics with titanium carbide or nitride improves frictional properties under oxidizing conditions via the formation of lubricous titanium dioxide on the surface under reasonable, therefore to expect that some ceramic/metal wear properties compared to the same ceramics sliding hot, oxidizing conditions (ref. 7). It appears combinations might have improved friction against themselves or another ceramic. and
The scope of the research reported in this paper includes the results of bench tests to measure the friction and wear of ceramics sliding against themselves and against a nickel base alloy, Inconel 1718. Tests temperatures were 25 to 800 C in air. MATERIALS Metal Alloy Inconel 718.-This is a nickel-chromium alloy that a 100-g indenter load. The nominal chemical composition Nb 5, Mo 3.1, Al 0.4 Si 0.3, Mn 0.2 and C 0.04. Oxide They Typical chemical compositions are further described below. and physical is precipitation hardened to H v -- 520 kg/mm 2 at by weight percent is: Ni 53, Cr 18.5, Fe 18.5, Ceramics properties of the oxide ceramics are listed in table I. Mullite.-Mullite is a mineral name for the stoichiometric composition 3A1203-2SIO 2. The material tested in this program is a commercial grade of mullite consisting of mullite and another phase. EDS spot analyses and XRD show that the microstructure consists of crystalline mullite cemented with a silica glass that contains substantial amounts of K, Ti, and F. This type of structure is common to many ceramics. The mullite tested in this program is very porous with only 84 percent of full density. The porosity contributes to a rough surface of 1 to 1.3/zm rms and is the roughest material tested. Alumina (aluminum oxide).-This grade of aluminum oxide, A1203. aluminum oxide crystal structure. is a sintered, polycrystalline, high purity, It contains traces of Fe203 and TiO 2. XRD Surface finish is 0.25 to 0.4/ m rms. fully-dense analyses reveals commercial an alpha Aluminum oxide-silicon carbide whisker composite.-This material is a commercial composite of alumina containing 25 vol SiC whiskers. The whiskers are 0.25 1.25/zm in diameter and are 5 to 12/ m long. XRD reveals alpha alumina and alpha SiC. The material is fully-dense and has a surface finish of 0.1 to 0.2/ m. Partially stabilize zirconia.-This is a transformation toughened material. It is designated by the supplier as the MS or maximum strength grade. The stabilizers are MgO and HfO T XRD and microstructural analyses reveal that the matrix has a cubic crystal structure with fine, ellipsoidal-shaped tetragonal precipitates uniformally dispersed in the cubic grains. A monoclinic phase also exists within these grains and at the grain boundaries. Porosity is 1 to 2 percent in the form of fine pores. Silicon Properties of the silicon-base ceramics Ceramics in this study are listed in table I. Silicon nitrid% (Sign).-This ceramic contains 8 percent Y203, tungsten, and magnesium. XRD shows a minor WSi 2 phase and a predominate beta-Si3N 4 phase. Surface roughness is 0.25 to 0.38 #m rms.
Silicon stoichiometric extremely carbide (SiC).-This is a sintered material with the alpha SiC crystal structure. It is highly with no excess Si. The microstructure is only very slightly porous and the material is hard with a typical Hv -- 2500. Surface roughness EXPERIMENTAL is 0.25 to 0.38. PROCEDURE Friction and wear tests were performed using a pin on disk specimen geometry. Some reference data from previously reported tests using a double rub block on disk specimen geometry are included for comparison (ref. 8). Detailed studies of ceramic rub blocks sliding on Inconel 718 disks are reported in references 9 and 10. Schematics of both specimen geometries are shown in figure 1. Friction is recorded continuously during each test duration of 1 hr. After each test, wear volumes are calculated from the diameters of the circular wear scars worn on the hemispherically of the worn surfaces of the disks. tipped pins and from profilometer The unit of wear in this paper is the wear factor, k, which is defined as the wear volume the product of the load and the sliding distance. The algebraic expression is: traces divided by k (ram) 3 (Nm) -1 The use of this factor implies that the wear volume is linearly proportional to the load and to the sliding distance. Although this assumption is an over-simplification, it has been found to be reasonable for a range of loads and sliding velocities over which the wear mechanism does not change. Comparison of wear factors allows one to estimate the relative wear resistance of various sliding combinations tested under identical conditions. The factors can also be used predictively with fair success when the wear mechanism in the application is the same as that in the tests used to obtain the k factors. The wear mechanisms for known combinations of speed and load can sometimes be predicted from published wear maps (e.g., refs. 11 and 12). If wear maps for the material combination are not available, the similarity of wear mechanisms in the test and in the application may be determined by comparative microscopic examination of the worn surfaces. Wear factorsin thisstudy variedfrom 10-3 to 10 --7 mm3/Nm with 10-3 indicatingunacceptably high wear forany application, and 10 -5 or lower (depending on wear rate requirements)needed for engineeringapplications. Wear is measured with a surfaceprofilorneter equipped with an area measuring computer program. Wear factorsare presentedas bar graphs in thispaper. Where replicate testswere performed, the top of each data bar isthe average of two or three testsand the errorbar isthe maximum wear factorin the data scatter. EXPERIMENTAL RESULTS AND DISCUSSION The friction and wear characteristics of oxide-base and of silicon-base ceramic/ceramic pairs were determined in air at temperatures from room ambient to 900 C (in a few tests to 1200 C). The friction and wear of alumina-base ceramic/metal combinations were also determined for comparison with the results for the corresponding ceramic/ceramic pairs.
Variable Temperature Experiments Friction coefficients for monolithic alumina against itself and against Inconel 718 are compared in figure 2(a). The experiments were conducted under relatively mild conditions of a 4.9 N load and a 0.38-m/s sliding velocity. Friction coefficients are very high for the ceramic/ceramic pair beginning at 0.60 -4- 0.10 (very erratic) at room temperature and steadily increasing with temperature to above 1.0 at 900 C. The friction coefficient for the ceramic/metal pair is about the same as that of the ceramic/ceramic pair at room temperature, but remains constant with increasing temperature to around 500 C, then drops dramatically to 0.3 t 0.03 at 750 and 900 C. This marked decrease in friction coefficient corresponds to the conditions at which an adherent nickel-chromium oxidation product forms on the wear track of the Inconel 718 disk. Analogous experiments were performed with alumina composites containing 25 wt% of SiC whis- kers. A similar effect of friction reduction by metal oxides is seen in figure 2(b). However, the beneficial effect on friction is much less than it is for monolithic alumina. This may be due to the abrasive action the SiC whiskers in more rapidly wearing away the metal oxides as they form. of The beneficial effect of metal oxidation products has been frequently observed and found to be quite general for turbine alloys in sliding contact under hot oxidizing conditions (e.g., ref. 5). Figure 3 from reference 8 shows that for three silicon base ceramics, three oxide base ceramics, and Inconel 718 rub blocks sliding against Inconel 718 disks, the friction coefficient is sharply reduced under hot, oxidizing conditions. While friction coefficients vary considerably for the different materials at room temperature, they are nearly identical at 800 C. We conclude that the oxides on the nickel-chromium alloy are lubricous and control the friction of all these sliding material combinations at 800 oC. Constant Temperature Experiments A series of tests were performed in order to obtain pin and disk wear factors kp and k d and a measure of the scatter in friction coefficients during tests of 1 hr duration at various constant temperatures. These tests were run at a higher sliding velocity and a higher load than were the ramped, variable temperature tests, the tests were at a load of 10 or 27 N and a sliding velocity of 2.7 m/s. The wear mode was found to be the same at 10 and 27 N. Therefore, the data are combined for tests at the two loads. Alumina base ceramics.-Figure 4(a) gives the friction-temperature characteristics of the alumina base ceramics: aluminum silicate (mullite), alumina, and alumina with 25 wt% SiC whiskers. Average friction coefficients for monolithic alumina is around 0.5 to 0.7 at all temperatures. Friction is about the same for the alumina-SiC composites but much more erratic with large scatter bands in the data. Friction coefficients for mullite are substantially lower in the range of abut 0.35 to 0.50 from room temperature to 800 C, and very steady with small scatter bands in the data. This may be attributed to the relatively low hardness of mullite (I'Iv 950) compared to alumina (H v 1606) and alumina-25 SiC (H v 2200). However, the lower hardness of mullite may be expected to result in higher wear. The wear factor data of figures 4(b) and (c) show that this is the case. The pin and disk wear factors are seen to be considerably higher than they are for alumina, which in turn wears more rapidly than the alumina-SiC composite. mullite Inconel friction Mullite on Inconel 718.-Figure disks; (2) Inconel 718 pins on 718 disks. Friction coefficients is about 20 percent higher for 5(a) compares the friction at 25 and S00 C of: (I) mullite pins on mullite disks; and (3) the reverse configuration of mullite pins on are the same for both metal versus ceramic configurations. At 25 C, the ceramic versus metal configurations than for mullite on mullite. 4
At 800 C, on the other hand, friction is lower for the ceramic versus metal pairs compared to mullite on mullite. This is consistent with the results from rub block on disk tests shown in figure 3 from reference 8. The lower friction at 800 C is attributable to the formation of lubricous oxides on Inconel 718 at high temperature. lower Pin and disk wear factors are shown in figures 5 (b) and (c). Wear factors for pins and disks at 25 C and at 800 C for mullite on Inconel 718 than for mullite versus mullite. are mullite, Alumina-25 SiC composite on Inconel 718.-Figure 5(a) shows that in contrast to the results with the specimen configuration has a strong influence on friction at 800 C. Metal oxidation did not have a beneficial effect for Inconel pins on composite disks, but did provide a substantial benefit for the reverse specimen configuration. Apparently, the composite abraded the metal oxide on the small, continuous contact area of the metal pins at too high a rate for a lubricous film to develop. The relatively large, discontinuous contact area on the metal disks however, allowed an adequate lubricous oxide film to develop. Wear factors are given in figures 5 (b) and (c). Although metal oxidation reduced friction for the composite pin versus metal disk geometry, it did not provide an equivalent benefit in reducing metallic wear. In general, composite wear was low and metal wear was high for this material combination. these Partially stabilized zirconia silicon three ceramics have characteristically carbid% and silicon nitride.-Figures 6 (a) and (b) show that high friction coefficients at all test temperatures. Friction coefficients for Si3N 4 is the highest overall averaging about 0.7 at room temperature and exceeding 0.8 at 400 and 800 C. Friction coefficients for SiC are consistently abut 20 percent lower. The scatter bands on the data show that the friction is moderately erratic during the duration of the tests. The friction coefficients for zirconia are also very high and considerably more erratic than for silicon carbide and silicon nitride. Wear factors are given in figures 6 (c) and (d). Wear is moderate are the surprisingly low pin and disk wear of SiC at room temperature at room temperature. to high in most cases. Exceptions and the low disk wear of zirconia The high friction and wear of ceramics sliding on ceramics has been reported by others (refs. 1 and 2). This study further confirms the critical need for suitable lubrication of ceramics if they are to be used as sliding contact bearing materials. It is known that high friction coefficients markedly increase surface tensile stresses within the sliding contacts of brittle materials (refs. 3 and 4). The high localized tensile stresses are largely responsible for the microfracture wear mode common in ceramics. In this study, we show that friction and wear of ceramics is less for ceramics sliding on a nickel-chromium turbine alloy than against a like ceramic counterface material. This is especially apparent under hot oxidizing conditions where lubricous oxides form on turbine alloys. CONCLUSIONS 1. Under most sliding conditions, unlubricated ceramics as a class exhibit high friction and wear. 2. Under hot, oxidizing conditions, friction and wear are considerably lower for ceramics sliding a nickel-chromium alloy (Inconel 718) than for ceramics sliding against a like ceramic counterface. on
3. Tenacious nickel-chromium oxide films are lubricous at high temperature for the monolithic- ceramic/metal combinations studied in this program. Less benefit is seen for a composite of alumina 25 vol% SiC whisker content, probably because the metal oxide film is abraded away by the SiC whiskers. with 4. The generally poor friction and wear properties of unlubricated ceramics emphasizes the need for additional research to develop lubricative coatings or surficial treatments for them. This is especially important in order to exploit the high temperature stability of ceramics in practical sliding contact applications. REFERENCES 1. Sutor, P.: "Tribology of Silicon Nitride Vol. 5, pp. 461-469, and Silicon Nitride-Steel Sliding paris," Cer. Engr. Sci. Proc., 1984. 2. Habig, K.H. and Woyt, M.: "Sliding Friction and Wear of Ai203, ZrO 2, SiC, and 5th International Conference on Tribology, Vol. 3, pp. 106-113, 1989. 3. Richerson, D.W., Lindberg, L.J., Carruthers, and SiC Interfaces," Cer. Engr. Sci. Proc., 4. Sliney, H.E. and Splavins, T.: "The Effect Induced Cracking in Aluminum Oxide, W.D., and Dahn, J.: "Contact Vol. 2, pp. 578-588, 1981. Si3N4," Stress of Ion-Plated Silver and Sliding Friction Vol. 49, No. 2, pp. 153-159, 1993. Proc. of the Effects in Si3N 4 on Tensile 5. Johnson, R.L. and Sliney, H.E., "Ceramic Surface Films for Lubrication at Temperatures 2000 F," Ceramic Bulletin of Am. Cerm. Soc., Voh 41, No. 8, pp. 504-508, 1962. 6. Lankford, J. and Wei, W.,: "Friction Sci., Vol. 23, pp. 2069-2078, and Wear Behavior of Ion Beam Modified Stress- to Ceramics," J. of Mat. 1987. 7. Gangpadhyay, A.K., Fine, M.E., and Cheng, H.S.: "Friction and Wear Characteristics of Titanium and Chromium Doped Polycrystalline Alumina," Lubr. Engr., Vol. 44, No. 4, pp. 330-334, 1988. 8. Sliney, H.E., Jacobson, T.P., Deadmore, Temperatures to 900 C," Cer. Engr. D., and Miyoshi, K.: "Tribology of Selected Ceramics and Sci. Proc., Vol. 7, Nos. 7-8, pp. 1039-1051, 1986. at 9. Deadmore, D. and Sliney, H.E., "Friction and Wear of Monolithic and Fiber Reinforced Silicon Ceramics Sliding against In-718 Alloy at 25 to 800 C in Atmospheric Air at Ambient Pressure," NASA TM-100294, Feb. 1988. 10. Sliney, H.E. and Deadmore, D.L., "Friction and Wear of Oxide-Ceramics Alloy at 25 to 800 C in Atmospheric Air, NASA TM-1002291, Aug. 11. Lim, 12. Wang, S.C. and Y.S., Ashby, Hsu, S.M., No. 1, pp. 63-69, M.F.: Acta and Munro, Metallurgica, R.G.: Sliding 1989. Against In-718 Vol. 35, p. 1343, 1987. Ceramic 1991. 6 Wear Maps: Alumina, Lubr. Engr., Vol. 47,
, Et 0 0 C 0 0 0 . 0 L o c3 t 3 ' e4 o r 0 -- . . . , . -. s -ao -a 0 . . o o o o Z Z O o E 0 0 o -- %z o 0 : o . o c c . E 0 c o v - : . . o 0 ' ' 7
J2o# 2o3 1.2 A. 0.8 - Rub shoes AI203/I-718 I 7 0.6 ,Load----- ----- Load 0.4 [a) Double rub shoe on disk. o. - I ) I (a) Monolithic I I I alumina. Rider.-. ) Applied i l'/ Wear tJr ck -' ml j AI203 25wt%SiC whiskers (like pair) ---O--- A1203 25wt%SiC whiskem/I-718 load Direction . o-" of rotation (b] Pin on disk. Figure 1.---Friction conngurationc 1.6 r- 1.2 1.0 and war test specimen o.4 ""'i I -"i . 0.8 """-'[ ""'"""'"'C] . "'" 0.2 0 200 400 600 Temperature, (b) SiC whisker Figure 2.--Comparative reinforced 1 I 800 1000 C alumina. friction-temperature characteristics during low velocity pin/disk tests of ceramicceramic and ceramic/metal pairs. Air atmosphere, 5N load, 0.38 m/s sliding velocity.
0.9 -- -----0----- Mullite ----O--- J2O3 0.8 . . AI203 25wt%SiC D O 0.7 T Data scatter 0 0 U 0.6 400 600 band 0 U 0.5 0.4 I 0.3 0 Temperature, 200 Temperature, C "E 0.8 I--" 1 0.7 0.6 800 1000 1200 1400 C (a) Friction. 25 (Metal 800 oxide controls 10-3 friction a 800 C) Temperature, C o 0.5 : 10 Q) o0.4 0 10-S o 0.3 "1 i, mE 25 Rs 350/400 r'n 12oo 0.2 10-S 0.1 l ,E md/ 550/ 00 z 0 SiC Si3N 4- Si3N 4- BY203 3Si2W AI203 Mullita Fused 10 7 1-718 E (b) Pin wear. quartz O Rub block material - 10-3 Figure 3.mFdction of various ceramics and of Inconel 718 sliding on Inconel 718 in air (50% R.H.) at room temperature and at 800 C, 0.18 m/s, 67 N load (from reference 8). 10-4 10-6 lO-S i I 10 7 Mullite AI203 AI203 25%SIC (c) Disk wear. Figure 4.---Friction and wear pin/disk data for like ceramic/ceramic pairs of alumina-based ceramics in air at 2.7 m/s. Note: each bar graph gives average in data scatter. 9 for 2 or 3 tests. Top of error bar is maximum
0.9 0.8 Tempera Jre, C 0.7 25 BOO e .9.0 0.6 0.5 O 0.4 iO f i. U. 0.3 0.2 0.1 0 (a) Friction. lO-3-10-4 10-S 10-S 10-7 E 10-8 ,E lO, E (b) Pin wear. o lO-6 lO-7 le-8 ,B M ullite vs. 6718 vs. Mullite vs. mullite mullite 1-718 AI20 3 25%SIC vs. 1-718 vs. AI203 25%SIC AI203 AI203 25%SIC vs. 1-718 25%SIC (c) Disk wear. Figure 5.--Friction and wear pin/disk for ceramic/metal pairs in air at 2.7 m/s. * Transfer of pin material resulted in negative wear factor. Note: Each bar graph gives average for 2 or 3 tests. Top of error bar is maximum l0 in data scatter.
Temperature, C 0 8 mm 10-3 -- 25 800 10 f 400 0.7 10-5 0.6 0.5 -- PSZ Data scatter T e .o O O o c O o I 0.4 I 10-S band E L (a) Partially-stabilized z I EE 10-7 E zirconia. (c)Pinwear. C O O 0.9 -- I' 0.8 10-3 - 10-4 -- 10-5 -- 0.7 0.6 s S T 0.5 0.4 0 ----0---- SiC --- Si3N 4 - --- 10-6 I I I I 200 400 600 800 Temperature, (b) Silicon-based Figure 6.--Friction I 10- 7 1000 SiC Si3N4 C ceramics. and wear characteristics (d) Disk wear. for like pairs of monolithic 1] ceramics in air at 2.7 m/s sliding velocity. PSZ
REPORT Public re burden for DOCUMENTATION t s'collect n of formabon Is estL, nated Form Approved OMB NO. 0704-0188 PAGE to average 1 hour pe response, includ g the time for reviewing instructions, searching extsbng data sources, ga hehng and maintldmng data needed, and completing and reviewing the collection of informaben. SerKI comments regarding this burden est mte or any other aspect of this oollection of information, including suggestions for reducing this burden, to Washingto Headquartm erdces, Dir torate tot Infownabon Operations and Reports. 1215 Jefferson Davis , Suite 1204, Arlington, VA 22202.4302, ar to the Otrce of Management and Budget, Papen rk Re uc on Proj mt (0704.-0188), Wa ington, IX; 2O503. 1. AGENCY USE ONLY (Leave blank) 3. REPORT TYPE AND DATES COVERED 12. REPORT DATE October 1993 Technical Memorandum 4. TITLE AND SUBTITLE 5. FUNDING NUMBERS The Friction and Wear of Ceramic/Ceramic Combinations in Sliding Contact 6. WU-505-63-5A AUTHOR(S) Harold 7. and Ceramic/Metal E. Sliney PERFORMING and Christopher ORGANIZATION National Lewis NAME{S) Aeronautics Research Cleveland, DellaCorte AI D and Space 8. PERFORMING ORGANIZATION REPORT NUMBER ADDRESS(F-S) Administration Center Ohio E-8121 44135-3191 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADORESS(ES) 10. SPONSORING/MONITORING AGENCY National Aeronautics Washington, 11. 12L SUPPLEMENTARY Prepared for the STLE-ASME Orleans, Louisiana, alloy. room ambient to 900 geometry. SUBJECT sponsored Responsible by the Tribologists person, Harold E. Sliney, and Lubricant (216) Engineers, New 433--6055. 12b. DISTRIBUTION CODE words) characteristics turbine attributed Conference 1993. DOE-UC-373 200 tribological than Tribology 24---27, 23 based tions TM-106348 DOE/NASA/50306-3 - Unlimited (Maximum contact NASA STATEMENT Category ABSTRACT The 14.' October DISTRIBUTION/AVAILABILITY Subject Administration 20546-0001 NUMBER NOTES Unclassified 13. and Space D.C. REPORT of ceramics sliding friction and wear of oxide C (in a few cases The In general, especially for ceramic/ceramic primarily to 1200 C) were at high temperature, combinations. to the lubricious on ceramics ceramics nature The better are compared to those and silicon-based measured friction and wear performance surface of the metal. were lower sliding on a nickel- in air at temperatures for a hemispherically-tipped triboiogical of the oxidized of ceramics ceramics pin from on a fiat sliding for ceramic/metal for ceramic/metal combina- combinations is lS. NUMBER OF PAGES TERMS 12 Ceramic friction; Ceramic wear; Ceramic/ceramic tribology; ceramic/metal tribology 16. PRICE CODE A03 17. SECURITY CLASSIFICATION OF REPORT Unclassified NSN 7540-01-280-5500 18. SECURITY CLASSIRCATION OF THIS PAGE Unclassified 19. SECURITY CLASSIFICATION 20. UMITATION OF ABSTRACT OF ABSTRACT Unclassified Stan0ard Form Prescribed 298-102 by ANSI 298 (Rev. Std. Z39-18 2-89)
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sliding velocity. Friction coefficients are very high for the ceramic/ceramic pair beginning at 0.60 -4-0.10 (very erratic) at room temperature and steadily increasing with temperature to above 1.0 at 900 C. The friction coefficient for the ceramic/metal pair is about the same as that of the ceramic/ceramic pair at
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Chính Văn.- Còn đức Thế tôn thì tuệ giác cực kỳ trong sạch 8: hiện hành bất nhị 9, đạt đến vô tướng 10, đứng vào chỗ đứng của các đức Thế tôn 11, thể hiện tính bình đẳng của các Ngài, đến chỗ không còn chướng ngại 12, giáo pháp không thể khuynh đảo, tâm thức không bị cản trở, cái được
Lecture Note Chapter 6 1. Overview: friction force Friction forces are categorized as either static or kinetic. The coefficient of static friction μs characterizes friction when no movement exists between the two surfaces in question, and the kinetic coefficient μk characterizes friction where motion occurs. s coefficient of static friction k coefficient of kinetic friction
FRICTION TESTING ASTM D 1894 "sled test" Coefficient of friction testing Does not determine wear resistance Can show slip/stick FRICTION TESTING RTP Modified ASTM D3702 Friction Test Oscillating motion used to measure Friction coefficients and Glide FactorSM Glide FactorSM is used to quantify the difference between µ s .
